1. Field of the Invention
This invention relates to bilayer rear projection screens comprising a supporting polymeric layer and an adhered polymeric layer, preferably tinted, containing specific light diffusing particles.
2. Description of the Prior Art
In recent television technologies, the size of screens for Braun tubes is limited to the size of less than 50 inches even in large screen type televisions because the inside of a cathode ray tube is vacuum. A larger TV screen can be used in rear projected displays. There are two types of projected displays, a rear projected type and a front projected type. Slides are generally used with the front projected type and white cloth or white plastic screens are commonly used as screens thereof. When a translucent sheet is used, a rear projection screen can also be used in viewing slides.
EPC publication 269,324, Jun. 1, 1988 and EPC publication 342,283, Nov. 23, 1989 disclose a plastic translucent sheet with excellent light transmittance. Further use of light diffusing compositions as rear projection screens is also disclosed in these publications.
The performance of a rear projection screen is judged by the balance in characteristics of resolution, gain and contrast. The screen is required to provide sufficient resolution to be useful in data presentation by displaying sharp images. At the same time, the screen must diffuse the light in such a way as to allow a broad viewing audience angle. A gray tint is typically used to create contrast. This contrast is most noticeable when images on the screen are viewed in the presence of ambient light. Typical screens consist of a sheet of acrylic polymer, i.e., poly(methyl methacrylate), or glass, approximately 6 mm thick and are coated with a thin (&lt;25 microns) layer of a light diffusing material. A neutral gray tint is sometimes added to the coating to provide improved contrast over screens without the tint.
The industry still seeks a light-weight, readily prepared, efficient rear projection screen with the specified light-scattering and transmission qualities.